 function Greeting({name}) {
    return (
        <div>
            <h1>Hello, {name}</h1>
        </div>
    )
 }
 function Child() {
    let list = {};
    return (
        <>
            <h1>Child</h1>
            {list.map((item, index) => {
                 <span key={index} >{item}</span>
            })} 
        </>
    )
 }
 function Main() {
    return (
        <>
            <Child/>
            <Greeting name="world" />
            <Greeting name="liheng" />
        </>
    )
 }

 export default Main;